1. Field of the Invention
The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having electrode extensions.
2. Discussion of the Background
Gallium nitride (GaN)-based light emitting diodes (LEDs) have been used for various applications, such as a natural color LED display device, an LED traffic signal, a white LED, or the like. Also, a high-efficiency white LED is expected to replace a fluorescent lamp.
In particular, the efficiency of the white LED reaches a similar level to the efficiency of the general fluorescent lamp.
A GaN-based LED is generally formed by growing epitaxial layers on a sapphire substrate, for example, and includes an N-type semiconductor layer, a P-type semiconductor layer, and an active layer interposed therebetween. Meanwhile, an N-electrode pad is formed on the N-type semiconductor layer and a P-electrode pad is formed on the P-type semiconductor layer. The electrode pads of the LED are electrically connected to an external power supply, which drives the LED.
Generally, the GaN-based semiconductor layers are grown on a single crystal substrate such as sapphire and then subjected to a chip separation process, thereby forming a single LED. In this case, the single crystal substrate is separated along a crystal surface, such that the substrate generally has a rectangular shape. Generally, the final shape of the LED limits a light emitting structure, for example, a mesa shape, an electrode pad shape, and a shape of the extensions extending from the electrode pad. For example, U.S. Pat. No. 6,650,018, issued to Zhao, et al., discloses extensions extending from electrode contacts in order to improve current spreading, wherein these extending parts generally extend in a straight line along an edge having a rectangular shape.
FIG. 1 is a plan view showing an LED according to the related art and FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1.
Referring to FIG. 1 and FIG. 2, the LED includes a substrate 21 and a mesa structure M. In addition, the LED includes a lower contact layer 23, an active layer 25, an upper contact layer 27, a transparent electrode layer 29, a first electrode pad 31, a second electrode pad 33, lower extensions 31a, 31b, and 31c, and upper extensions 33a and 33b. 
The lower extensions 31a and 31c extend from the first electrode pad 31 and the lower extensions 31b extend along the edge of the substrate 21 from the lower extensions 31a. Further, the lower extension 31c extends from the first electrode pad 31 towards the second electrode pad 33. The lower extensions 31b and 31c are parallel with each other and the lower extensions 31a extend in a direction crossing with the lower extensions 31b and 31c. 
Meanwhile, the upper extensions 33a extend from the second electrode pad 33 and the upper extensions 33b extend from the upper extensions 33a, respectively. The upper extensions 33a are parallel with the lower extensions 31a and the upper extensions 33b are parallel with the lower extensions 31b and 31c. The upper extensions 33b each extend to a region between the lower extension 31b and the lower extension 31c. 
According to the related art, the lower extensions 31a, 31b, and 31c are disposed on the lower contact layer 23 and the upper extensions 33a and 33b are disposed on the upper contact layer 27, thereby making it possible to improve current spreading capability in the LED. However, since there is a space formed between the lower extensions 31a, 31b, and 31c and the mesa structure M in order to form the lower extensions 31a, 31b, and 31c, the region of the mesa structure M is reduced by a larger area than the region of the lower extensions. As a result, the light emitting area of the LED may be reduced due to the formation of the lower extensions 31a, 31b, and 31c. In addition, the light emitting area may be reduced, since the lower extensions 31b are formed to enclose the upper extensions 33b and the lower extensions 31a connecting the lower extensions 31b to the first electrode pad 31 are required.